1Department of Mining Engineering, Isfahan University of Technology, Iran

2Department of Civil Engineering, Isfahan University of Technology, Iran

چکیده [English]

SummaryThe fatigue behavior under completely reversed loading for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx, which have different mineral compositions and formation conditions, were evaluated using a new developed apparatus. The obtained S-N curves followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, the endurance limit is perceived for both tested rocks as well as observed in ferrous metals. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively.

IntroductionDuring fatigue phenomenon cyclic loading causes a material to fail prematurely and suddenly like a brittle failure at a stress level less than determined strength under monotonic condition. Rock formations and structures such as faults, joints, bedding planes, underground reservoirs, tunnels walls, bridge abutments, roads and dams’ foundations, etc. can be subjected to dynamic loadings resulting from vibrations of the earth’s crust, through major earthquakes, rock bursts, rock blasting and drilling and also, traffic. Reaction of rocks to cyclic and repetitive stresses resulting from dynamic loads has been generally neglected with the exception of a few rather limited studies. In this research work, the fatigue behavior of two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were studied under completely reversed loading.

Methodology and ApproachesThe stress-life method was applied and fatigue behavior and the existence of the endurance limit for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were evaluated using a new developed apparatus. The developed fatigue testing machine was inspired by rotating beam fatigue testing machine (R. R. Moore) which is commonly used for laboratory fatigue test in metals.

Results and ConclusionsThe obtained results (S-N diagram) followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, results showed that both rocks have endurance limit. The results also illustrated that the endurance limits for both tested rocks are ranged between 0.4 and 0.6 of their tensile strengths. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively. The agreement between the obtained results and presented results in fatigue of other materials showed that the offered method can be applied for studying the fatigue of rocks.